The present invention relates to a process for fabricating superconducting ceramics materials comprising a yttrium-including rare earth element, an alkaline earth metal and copper oxide (hereinafter referred to as "R-A-Cu-O based ceramics") which has a high theoretical density ratio and thus has a high critical current value.
Conventional processes for fabricating worked materials such as wire rods, plates, strings, coils, and ribbons made of an R-A-Cu-O based superconducting ceramics include a process in which starting powders, i.e., an R.sub.2 O.sub.3 powder, an alkaline earth metal carbonate powder, and a CuO powder, each having an average grain size of not greater than 10 um, are provided and compounded in a predetermined compounding ratio followed by mixing and compacting them to obtain a compacted body, which is then calcined, e.g., in an atmosphere of dry air, at a temperature of from 850.degree. C. to 950.degree. C. to form a superconducting ceramics having a composition of YBa.sub.2 Cu.sub.3 O.sub.7, for example, the ceramics is then ground to obtain powder of an average grain size of not greater than 10 um and filled in a pipe of silver (Ag) or copper (Cu), and the pipe filled with the ceramics powder is molded into a worked material of a predetermined shape by cold processing such as swaging, rolling with grooved rolls, and processing with a die.
With the above-described conventional processes, it is very difficult to fill superconducting ceramics powder in a metal pipe in a filling ratio of not lower than 50% when fabricating processed superconducting materials or members. Further, it is noted that worked materials fabricated using such compacted body of a low filling ratio when cold processed have a theoretical density ratio of at most about 90%. In addition, it is also difficult upon calcination to fabricate superconducting ceramics with an oxygen content as high as up to 100% of theoretical content, and the resulting suerconducting ceramics tends to lack oxygen. For example, when fabrication of YBa.sub.2 Cu.sub.3 O.sub.7 is contemplated, product has a composition of YBa.sub.2 Cu.sub.3 O.sub.7-d where d indicates degree of deficiency of oxygen. Under the circumstances, high critical current value and high critical temperature of superconducting ceramics worked materials cannot be secured with the conventional processes.
Further, when the above conventional superconducting ceramics material is worked into wire rods and then into coils it tends to suffer decrease in critical current value presumably due to heterogeneity in the density of filled superconducting ceramics powder and/or poor contact or non-contact between the respective grains of superconducting ceramics powder as the result of gap formed or slipping between the grains during working into coils.